1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a driving method thereof for controlling an angle at which an image is viewed.
2. Discussion of the Related Art
In general, an LCD device controls light transmitted through liquid crystals in accordance with video data to display an image corresponding to the video data. The LCD device makes possible a large sized screen beyond a limit, a slim profile, and lightweight. Accordingly, the LCD device is commonly used as a display device for computers and television receivers as a substitute for cathode ray tube (CRT) display devices.
Recently, users of portable devices such as portable phones, personal digital assistants (PDAs), and portable computers have a desire to prevent the data being displayed on the portable device from being viewed by other people. Therefore, it is desirable for LCD display devices in portable devices to include a narrow viewing angle mode as well as a normal viewing angle mode so that privacy and security can be achieved.
To achieve viewing angle control, a liquid crystal panel with viewing angle control mode includes a separate interference subpixel added to a color pixel. An example of a liquid crystal panel with viewing angle control mode includes a double structure liquid crystal panel. As shown in FIG. 1, a double structure liquid crystal panel includes a normal panel 10 in which color pixels are formed, and an interference panel 12 located on the normal panel 10. The interference panel 12 includes interference subpixels. The normal panel 10 is used for displaying an image while the interference panel 12 blocks light propagating in a lateral direction of the normal panel 10. In other words, the double structure liquid crystal panel switches between viewing angle modes of an image by blocking light propagating in a lateral direction of the normal panel 10 using the interference panel 12.
An LCD device with the double structure liquid crystal panel controls a viewing angle by selectively driving the interference panel 12 to select between a wide viewing angle mode and a narrow viewing angle mode. In other words, the LCD device turns on or off the interference panel 12 depending on the desired viewing angle mode. However, because external light needs to pass through the double liquid crystal layer in the above-described double structure liquid crystal panel, brightness of an image is significantly decreased. Additionally, the double structure liquid crystal panel has increased thickness and weight.
An alternative viewing angle control mode liquid crystal panel includes a region division-type liquid crystal panel in which color pixels and interference subpixels are arranged on the same plane. Color pixels on the region division-type liquid crystal panel include red, green, and blue subpixels as well as interference subpixels. Since the interference subpixels and the color subpixels are arranged on the same plane, the region division-type liquid crystal panel does not increase the thickness and weight of the panel. Also, since the region division-type liquid crystal panel controls the viewing angle using only one liquid crystal layer, the amount of light, brightness, and color purity are not diminished.
An LCD device including a viewing angle control mode liquid crystal panel selectively drives interference subpixels on the viewing angle control mode liquid crystal panel to display an image at a normal viewing angle and at a narrow viewing angle. In other words, only the color subpixels are driven when the LCD device displays an image at a normal viewing angle. On the other hand, the color subpixels and the interference subpixels are driven when the LCD device displays an image at a narrow viewing angle. A related art LCD device that controls the viewing angle using interference subpixels increases the brightness using interference subpixels according to a predetermined pattern during a narrow viewing angle mode by driving interference subpixels and color subpixels simultaneously.
In the related art LCD device that controls the viewing angle using interference subpixels, the increased brightness of interference subpixels according to the predetermined pattern effectively prevents viewing of images with outlines having a large degree of brightness change, such as a text including letters, from a lateral side. However, it is difficult to block an image with a small degree of brightness change, such as a picture, from being viewed from the lateral side. In addition, since the pattern is fixed, text images with small outline changes may be viewed, though dimly, from the lateral side. Accordingly, maintaining confidentiality and security of displays regardless of the kind of an image have been difficult in the related art LCD device with viewing angle controls.